The present invention relates to an apparatus and method for protecting the neurovascular bundle during cryoablation of tissues of the prostate. More particularly, the present invention relates to heating the vicinity of the neurovascular bundle while cooling pathological tissues in or near the prostate to cryoablation temperatures, thereby cryoablating pathological tissues while protecting the neurovascular bundle from damage. Additionally, the present application relates to a cryoprobe having a distal treatment head and a proximal shaft, which shaft is designed and constructed to protect tissues adjacent to the shaft from damage by cooling induced by cold gases exhausting from the distal treatement head.
In recent years, cryoablation of pathological tissues has become an increasingly popular method of treatment of prostate cancer and of benign prostate hyperplasia (“BPH”). Cryoablation of pathological tissues is typically accomplished by utilizing imaging modalities such as x-ray, ultrasound, CT, and MRI to identify a locus for ablative treatment, then inserting one or more cryoprobes into that selected treatment locus, and cooling the treatment heads of those cryoprobes sufficiently to cause the tissues surrounding the treatment heads to reach cryoablation temperatures, typically below about −40° C. The tissues thus cooled are thereby caused to loose their functional and structural integrity. Cancerous cells cease growing and multiplying, and cryoablated tumor tissue material, whether from malignant tumors or from benign growths, is subsequently absorbed by the body. Cryoablation may thus be used to treat malignant tumors of the prostate, and to reduce prostate volume in cases of BPH.
The principle danger and disadvantage of cryosurgical ablative treatment of the prostate, however, is the danger of partially or completely destroying the functional and structural integrity of non-pathological tissues proximate to the treatment locus, thereby having a deleterious effect on the health and quality of life of the treated patient.
Various devices and methods have been proposed to enable cryoablation of pathological prostate tissue while limiting damage to non-pathological tissue. These fall roughly into two categories: devices and methods which protect tissues by preventing excessive cooling of those tissues during a cryoablation procedure in their vicinity, and methods devices and methods which enable accurate placement of cryoprobes used in cryoablation, so as to successfully concentrate the cooling effect of such cryoprobes at or near pathological tissue, thereby minimizing unwanted cooling of non-pathological tissue.
An example of the former category is the well-known technique of introducing a heating device or a heated fluid into the urethra of a patient, to heat the urethra and tissues adjacent to it during cryoablation of portions of the prostate, thereby helping to protect the urethra from damage while prostate tissues nearby are being cooled to cryoablation temperatures.
An example of the latter category is provided by U.S. Pat. No. 6,142,991 to Schatzberger. Schatzberger describes a high resolution cryosurgical method and device for treating a patient's prostate, including the steps of (a) introducing a plurality of cryosurgical probes to the prostate, the probes having a substantially small diameter, the probes being distributed across the prostate, so as to form an outer arrangement of probes adjacent the periphery of the prostate and an inner arrangement of probes adjacent the prostatic urethra; (b) producing an ice-ball at the end of each of said cryosurgical probes, so as to locally freeze a tissue segment of the prostate.
Schatzberger's apparatus includes (a) a plurality of cryosurgical probes of small diameter, the probes being for insertion into the patient's organ, the probes being for producing ice-balls for locally freezing selected portions of the organ; (b) a guiding element including a net of apertures for inserting the cryosurgical probes therethrough; and (c) an imaging device for providing a set of images, the images being for providing information on specific planes located at specific depths within the organ, each of said images including a net of marks being correlated to the net of apertures of the guiding element, wherein the marks represent the locations of ice-balls which may be formed by the cryosurgical probes when introduced through said apertures of the guiding element to said distinct depths within the organ.
Thus, Schatzberger's method and apparatus enable a surgeon to place a set of cryoablation probes within a prostate with relatively high accuracy, and to operate those probes to ablate selected tissues while avoiding, to a large extent, inadvertent and undesirable ablation of healthy tissues near the ablation site.
However, neither Schatzberger's technique nor any other known technique has proven sufficiently accurate to prevent damage to peripheral tissues in all cases. In particular, the neurovascular bundle, a prostatic area rich in blood vessels and in nerve tissues having cardinal importance in the process of erection of penis, is particularly vulnerable to damage by conventional prostatic cryoablation procedures. The neurovascular bundle lies dorsolateral to the prostate from the level of the seminal vesicles to the urethra, and is embedded in the lateral pelvic fascia along the pelvic side wall.
Damage to the neurovascular bundle may cause loss of sexual potency. Potent patients having an active sexual life are understandably reluctant to risk loss of potency as a result of cryosurgical treatment of the prostate, and such loss of potency unfortunately occurs in a non-negligible percentage of patients treated with conventional cryosurgery, as it does also in cases of treatment of prostate tumors by non-cryosurgical means.
Thus, there is a widely felt need for, and it would be highly advantageous to have, a therapeutic approach to malignant prostate tumors and to benign prostate hyperplasia, which approach enables cryoablation of prostate tissues while protecting the neurovascular bundle, thereby substantially reducing or eliminating the danger that cryosurgical treatment of the prostate will cause loss of erectile potency of the patient.
Similarly, there is a widely felt need for, and it would be highly advantageous to have, apparatus and method enabling selective protection of sensitive and functionally important healthy tissues in close proximity to pathological tissues whose cryoablation is desired, in numerous similar contexts.
Referring again to Schatzberger's technique, clinical practice has revealed an unanticipated limitation of that technique, with regard to implementation using a dense array of small diameter cryoprobes. As will be discussed in greater detail below, Schatzberger's technique provides for coordinated insertion of a multiplicity of parallel probes into an organ, and in particular provides for percutaneous insertion of multiple parallel cryoprobes, through the perineum of a patient, into a prostate. However, cold gases exhausting from treatment heads of cryoprobes cool the shafts of those cryoprobes. Body tissues lying alongside cryoprobe shafts, although distant from an intended cryoablation target, risk being damaged by cold induced by contact with, or proximity to, cryoprobe shafts cooled by gases exhausting from cryoprobe treatment heads, where those gases have been intensively cooled, typically either by evaporation or by expansion through a Joule-Thomson orifice.
Schatzberger's technique has proven an important contribution to cryoablation technology, in that it provides means for high-resolution cryoablation specifically adapted to the three-dimensional form of an intended ablation target. A Schatzberger template in current use today presents a 13 by 13 array of apertures for insertion of cryoprobes, the apertures being separated by 5 mm from each other, and each probe being of 1.5 mm in diameter. Yet, in practice, clinicians do not typically place cryoprobes in adjacent apertures when using Schatzberger's template, but rather typically leave one or even two vacant apertures between each aperture utilized to insert a cryoprobe.
Thus, in typical clinical practice today, Schatzberger's apparatus is utilized at a lower resolution than that of which the apparatus is mechanically capable. Aside from a natural desire on the part of the surgeon to minimize puncture trauma to the perineum, the practice of sparse, rather than dense, utilizing of Schatzberger's template has to do with undesired cooling induced in the shafts of the inserted cryoprobes during ablation of the intended target. When multiple parallel shafts of cryoprobes are densely introduced into a perineum or other area not intended for cryoablation, and each shaft is cooled by cold exhaust gases exhausting from a treatment head of a cryoprobe, the cumulative cooling effect of the dense array of shafts is to cool tissues proximate to the cryoprobe shafts to an extent which is damaging to those tissues. To avoid such damage using prior-art cryoprobes, clinicians are obliged to use Schatzberger's template at a lower resolution than would otherwise be possible.
There are, however, clinical indications that dense rather than sparse use of Shatzberger's template would be desirable. There is, first of all, the generally recognized purpose of that template as it was described by Schatzberger, namely using a dense array of probes to provide small iceballs from each probe, thus enhancing accuracy of the ablation and limiting ablation to the intended target. Clearly, the more densely packed the array, the smaller the iceball needing to be induced by each probe, and consequently the more accurate the match between the zone of induced ablation and the desired cryoablation target.
In addition, however, there are now clinical indications that effective cryoablation of cancer may require more intense cooling than that provided by standard cryoablation procedures in common practice today. Andrew A. Gage and John G. Baust, in an article entitled “Cryosurgery—A Review of Recent Advances and Current Issues” appearing in CryoLetters 23, 69-78 (2002) published by the Royal Veterinary College of London, reports experimental results obtained by Clarke and associates and reported in Cryobiology 42, 274-285, wherein surviving cancer cells were cultured from tissues subsequent to cryoablation at temperatures below −50° C., despite the fact that temperatures below −50° C. are generally considered to be adequate for complete ablation of tissue. Gage summarizes an in vitro investigation of a human prostate cell (PC3) line as follows: “Cell survival was evaluated by culture . . . when cell cultures were exposed to freezing to temperatures of −25° C. to −80° C., 90-99% loss of viability was produced, but some cells repopulated twelve days post-thaw. A temperature of −100° C. was required to achieve total destruction.” According to Gage, similar results are reported by Clarke et al. in Mol Urol 159, 1370-1374 and by Hollister et al. in Mol Urol 2, 13-18. Gage also cites seven studies substantiating his summary that “The incidence of persistent disease after cryotherapy vary with case selection and different physicians, but generally is about 10-30%, as manifested by prostate specific antigen (PSA) values and positive biopsies three to four years after treatment.” These considerations, taken together, seem to indicate that improved cryoablation techniques are to be sought, both in ablation of prostate cancer and in other contexts.
It is generally recognized in cryoablation research and practice that the more intense the cold, the more reliable the ablation. It is further generally recognized that rapid cooling is an important factor in provoking cell death, a popular hypothesis being that rapid cooling encourages growth of intra-cellular ice crystals, known to be a powerful destructive agent, whereas gradual cooling tends to create extra-cellular ice crystals, which have some destructive effect but which are known to be less effective in ablation than are intra-cellular ice crystals.
It is further well known that proximity to a cryoprobe is a factor determining speed of cooling. Tissues adjacent to a rapidly cooled cryoprobe are cooled rapidly, whereas tissues more distant from a rapidly cooled cryoprobe are cooled more slowly.
Collectively, the above-mentioned clinical considerations give support for a hypothesis that massive rapid cooling by a dense array of small cryoprobes will provide improved survivability in cryoablation of prostate cancer and of cancers of other organs.
Yet, use of such a dense cooling array of cryoprobes cannot be undertaken with impunity under prior art methods and techniques such as those described by Schatzberger, because of the damage to tissues external to the intended cryoablation target, particularly damage to tissues cooled by proximity to a dense array of cryoprobe shafts transporting exhausting expanded cooling gases away from a dense array of cryoprobe treatment heads.
Thus there is a widely recognized need for, and it would be highly desirable to have, apparatus and method enabling cooling of cryoprobe treatment heads while preventing cooling of tissues adjacent to cryoprobe shafts, particularly in applications utilizing a dense array of cryoprobes.
In this context it is noted that U.S. Pat. No. 5,800,487 to Mikus et al. and U.S. Pat. No. 5,800,488 to Crockett teach a cryoprobe having a coolable treatment head comprising a heatable region, yet the probes mentioned therein do not comprise a heatable shaft, nor do they address, nor provide a solution to, the clinical need defined hereinabove. Additional art of relevance include U.S. Pat. No. 6,505,629 to Mikus et al.